How do we feel heat?

What happens to our cells and nervous system when they’re heated that allows us to sense the temperature?

Is it limited to certain frequencies (like infrared) or does it sense any increase in energy?

We have several types of heat sensors in our nervous system. They are triggered by heat energy, not by radiation, so it doesn’t matter what frequency incoming electromagnetic radiation is responsible for the heat, or if the heat enters the body through conduction or convection.

Heat, cold, and pain are all sensed through what are called Transient receptor potential (TRP) channels. Basically, the channels respond to heat and allow ions to flow into neurons, which our nervous system interprets as a heat sense. There are several different types of TRP channels in humans. The ones responsible for heat are called TRPA1, TRPM8, TRPV1, TRPV2, TRPV3, and TRPV4. These cover a wide range of temperatures. In order of coldest to warmest, they go TRPA1, TRPM8, TRPV4, TRPV3, TRPV1, TRPV2.

The last two, TRPV1 and TRPV2, trigger a pain response. TRPV1 kicks on at about 45 deg C, where TRPV2 kicks on at about 50 deg C (just below where tissue damage actually starts to occur). TRPV1 also reacts to capsaicin, which is why hot peppers feel “hot” to us. Many animals lack the TRPV1 sensor and can eat hot peppers without feeling the “hot”.

TRPA1 also triggers a cold pain response.

That’s 122F, which doesn’t sound hot enough to cause tissue damage. I’m sure my coffee is hotter than that, and I’ve heard of saunas hotter than that.

In a sauna, you’re sweating furiously to keep your tissues below that temperature, and you don’t stay in there for long. If your tissues get up to the same temperature as the sauna, then yes, you’ll suffer damage from it.

But its when that channel first starts warning about anything !. Its really saying “thats almost blistering hot !”.

112F water can cause burns to a new born babys skin in AROUND 8 minutes exposure… ( Don’t test this for yourself.)

And … as far as they know, no one ever survived with a core body temperature above 116F …
well many people become brain damaged from even lower fever than that.

You can get a 3rd degree burn from 120 degree water with about 10 minutes exposure. 3rd degree means permanent damage.

Nice link, Isilder.

Slight tangent to the OP, but what causes us to feel “cold” by eating peppermint? For example, the sensatoin when eating a Peppermint Pattie - mouth “feels” cold, but the food itself was probably just below room temperature. What is going on there?

The menthol in the peppermint hits the TRPM-8 receptors, the same ones used for cold-ness detection

Cool! Ignorance fought.